The present invention relates to a method for the production of quartz glass which has excellent plasma erosion resistance and can be used for semiconductor production. Furthermore, the invention relates to a mixed powder which can be used in the production of the said quartz glass.
In the production of semiconductors, for example in the production of semiconductor wafers, treatment efficiency has been improved in recent years by increasing the diameter and using plasma reaction apparatus for etching processes and the like. For example, in the semiconductor wafer etching process the etching treatment has been carried out using a plasma gas, such as fluorine-(F) based plasma gas for example.
However, when conventional quartz glass is located in an F-based plasma gas atmosphere, for example, the F-based plasma gas reacts with the SiO2 at the quartz glass surface and SiF4 is produced and this has a boiling point of −86° C. and so volatilizes readily and the quartz glass is eroded in large amounts and becomes thin and the surface becomes rough, and this material is unsuitable for use as jigs in F-based plasma gas atmospheres.
In this way conventional quartz glass gives rise to serious problems with erosion resistance, which is to say plasma erosion resistance, with plasma reactions, and specially in etching treatments in which F-based plasma gas is used, in semiconductor production. Hence improvement of the plasma erosion resistance by coating aluminium or an aluminium compound on the surface of the quartz glass parts has been proposed (Patent Citations 1 to 3), and plasma erosion resistant glass where the plasma erosion resistance has been improved by including aluminium in quartz glass has also been proposed (Patent Citation 4).
Adopting this procedure, a mixture of 5 wt % alumina powder in quartz powder was heated and fused under vacuum, quartz glass was formed and the plasma erosion resistance was investigated. When this was done the etching rate was from 40 to 50% lower than that of completely undoped quartz glass parts.
With this material, the boiling point of the AlF3 which is produced on reacting with an F-based plasma gas is 1290° C., a much higher temperature than that of SiF4 and so, while on the one hand the SiF4 part is greatly eroded, the AlF3 part does not volatilize to any great extent at the surface and it is thought that this is why the difference in the etching rates is so great.
The following documents represent the prior art: Japanese Unexamined Patent application Laid Open H9-95771, Japanese Unexamined Patent application Laid Open H9-95772, Japanese Unexamined Patent application Laid Open H10-139480, Japanese Unexamined Patent application Laid Open H11-228172.